Extruded fiver reinforced cementitious products having stone-like properties and methods of making the same

ABSTRACT

A cementitious composite product that can function as a substitute for stone and solid surface materials, such as granite, marble, and engineered stone is provided. Furthermore methods for manufacturing the cementitious composite product using an extrudable cementitious composition that can be extruded or otherwise shaped into stone-like building products that can be used as a substitute for many known stone products is disclosed. In one embodiment, the cementitious composite products can be manufactured more cheaply to be as tough or tougher and more durable than stone and solid surface materials.

BACKGROUND OF THE DISCLOSURE

The present disclosure relates generally to cementitious buildingproducts that contain high amounts of reinforcing fibers and moreparticularly, to extrudable compositions for use in making ultra-highstrength cementitious composite building products having stone-likeproperties.

The success of the building and construction industry is in large partdetermined by the properties available for use in construction. Manymaterials have been used historically and currently but each has one ormore significant limitations, as further described in the followingchart.

Specific Value Flexural Bulk Installed (Flexural Building StrengthDensity Cost/kg Strength/Installed Brittleness Good Materials [MPa][g/cm³] [US$/kg] Cost/kg) [Y/N] Aesthetics Wood 75 0.5 4 18.75 N YEternit 10 1.4 4 2.5 N N Steel 400 7.9 20 20 N N Concrete 3 2.3 0.1323.08 Y N Granite/Marble 18 2.5 6 3.0 Y Y Fiber 30 1.3-2.3 0.50 60 N Yreinforced cementitious product

As the availability of high quality natural occurring materials such asstone and wood become scarcer, the need for manufactured productsbecomes increasingly more important. Specifically, there is a need inthe design and construction of buildings with concrete and steel formanufactured products having high durability, low cost, high strengthand toughness per unit of mass, and that are aesthetically pleasing.

Moreover, in conventional building products, 90% of the concrete massand volume is required just to support itself in position and shape;only 10% is actually used in the dynamic or live loading capacity of thestructure. Similarly, 75% of the mass and volume of steel used in abuilding is to support itself and hold its position and shape; only 25%is actually used in the dynamic or live loading capacity of thestructure. Furthermore, although concrete has historically beenrecognized as having high compressive strength, the compressive strengthof concrete is not usable. Rather, it is its flexural or tensilestrength that is required, and the flexural or tensile strength is solow that in most cases it is assumed to be zero.

Based on the foregoing, it would be a great advantage and advance in theconstruction industry to have cementious product that could be moldedand shaped locally but would have a much higher flexural and tensilestrength so that little or no steel reinforcing would be required in thestructure. It would be a further advantage if such cementitious materialwould be of a lower bulk density and have a much improved bulk densityratio. This would increase the amount of concrete available for thedynamic loading capacity of the building.

Previous attempts to use fiber reinforcing concrete have been generallylimited by many factors. One factor is the difficulty of uniformlymixing and distributing fibers more than 3% by volume throughout a highstrength water cement ratio composition. The second factor is the rapidreduction in rheology of the concrete makes the shaping and placing ofthe concrete material much more difficult.

Accordingly, it would be advantageous to provide a cementitiouscomposite product and method for making the cementitious compositeproduct to be used in building products as a cost-effective substitutefor stone and solid surface materials. The cementitious compositeproduct could be manufactured to be tougher and more durable (i.e., lessbrittle) than stone and solid surface materials without usingreinforcing members such as rebar. Moreover, it would be beneficial toprovide cementitious composite products that could be used as asubstitute for stone materials.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to cementitious composite products (alsoreferred to as building products or cementitious composite buildingproducts) that can function as a substitute for stone and solid surfacematerials. Specifically, the disclosed compositions and manufacturingprocesses have an increased flexural and tensile strength by more than10 times as compared to conventional products. The products provide foreasy molding and shaping for a wide variety of usable constructionmaterials or products. Further, the compositions and processes makecementious building materials that are highly aesthetically pleasing ata much reduced cost and weight. These cementious materials are notbrittle and do not chip or crack like natural synthetic stone commonlyused in construction. Additionally, they have all the advantages ofstandard Portland Cement Concrete but are 10 times stronger and 100times tougher at ⅓ less weight. The products are non flammable, highlydurable and can be manufactured locally. A final advantage of thesematerials is that they obtain all required strength for use within 24 to48 hours and do not need the typical 28 day period of other cementitiousmaterials peak performance requirement.

Accordingly, in one aspect, the present disclosure is directed to acementitious composite product having stone-like properties. The productcomprises an extrudable cementitious composition comprised of ahydraulic cement, aggregate, a rheology-modifying agent, and fiberssubstantially homogeneously distributed through the extrudablecementitious composition and included in an amount greater than about 2%(by volume of the extrudable cementitious composition). The cementitiouscomposite product has a hardness value of at least 4 MOH and a bulkdensity of from about 1.3 g/cm³ to about 2.3 g/cm³.

In another aspect, the present disclosure is directed to a method formanufacturing a cementitious composite product having stone-likeproperties. The method comprises: mixing together water, fibers and arheology-modifying agent to form a fibrous mixture in which the fibersare substantially homogeneously dispersed; adding a mix of hydrauliccement and aggregate to the fibrous mixture to yield an extrudablecementitious composition having a plastic consistency and which includesfiber at a concentration greater than about 2% by volume of extrudablecementitious composition; extruding the extrudable cementitiouscomposition into a green intermediate extrudate having a predefinedcross-sectional area, the extrudate being form-stable upon extrusion andcapable of retaining substantially the cross-sectional area so as topermit handling without breakage; and causing or allowing the hydrauliccement to cure to form the cementitious composite product, wherein thecementitious composite product has a hardness value of at least 4 MOHand a bulk density of from about 1.3 g/cm³ to about 2.3 g/cm³.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram that illustrates an embodiment of anextruding process for manufacturing a cementitious composite buildingproduct;

FIG. 1B is a schematic diagram that illustrates an embodiment of anextruding die head for manufacturing a cementitious composite buildingproduct having a continuous hole extending therethrough;

FIG. 1C is a perspective view that illustrates embodiments of thecross-sectional areas of extruded cementitious composite buildingproducts; and

FIG. 2 is a schematic diagram that illustrates an embodiment of aroller-extrusion process for manufacturing a cementitious compositebuilding product.

DETAILED DESCRIPTION OF THE DISCLOSURE

It has been found that cementitious composite products can be made tohave stone-like properties so as to be cheaper and more durablesubstitutes for stone and solid surface products, such as countertops,tiles, cladding, roof tiles, and the like, as well as othernon-architectural products such as pre-cast and pre-formed materials.The terminology employed herein is used for the purpose of describingparticular embodiments only and is not intended to be limiting.

The terms “aggregate” and “aggregate fraction” refer to the fraction ofconcrete which is generally non-hydraulically reactive. The aggregatefraction is typically comprised of two or more differently-sizedparticles, often classified as fine aggregates and coarse aggregates.

As used herein, the terms “fine aggregate” and “fine aggregates” referto solid particulate materials that are sized at less than 5 mm.

As used herein, the terms “coarse aggregate” and “coarse aggregates”refer to solid particulate materials that are retained on a Number 4sieve (ASTM C125 and ASTM C33). Examples of commonly used coarseaggregates include ⅜ inch rock and ¾ inch rock.

The term “multi-component” refers to fiber-reinforced extrudablecementitious compositions and extruded composite products preparedtherefrom, which typically include three or more chemically orphysically distinct materials or phases. For example, these extrudablecementitious compositions and resulting building products can includecomponents such as rheology-modifying agents, hydraulic cements, otherhydraulically settable materials, set accelerators, set retarders,fibers, inorganic aggregate materials, organic aggregate materials,dispersants, water, and other liquids. Each of these broad categories ofmaterials imparts one or more unique properties to extrudatecompositions prepared therefrom as well as to the final product. Withinthese broad categories it is possible to further include differentcomponents (such as two or more inorganic aggregates or fibers) whichcan impart different, yet complementary, properties to the extrudedproduct.

The terms “hydraulically settable composition” and “cementitiouscomposition” are meant to refer to a broad category of compositions andmaterials that contain both a hydraulically settable binder and water aswell as other components, such as aggregates and fibers, regardless ofthe extent of hydration or curing that has taken place. As such, thecementitious materials include hydraulic pastes or hydraulicallysettable compositions in a green state (i.e., unhardened, soft, ormoldable), and a hardened or cured cementitious composite product.

The term “homogeneous” is meant to refer to a composition to be evenlymixed so that at least two random samples of the composition haveroughly or substantially the same amount, concentration, anddistribution of a component.

The terms “hydraulic cement,” “hydraulically settable binder,”“hydraulic binder,” or “cement” are meant to refer to the component orcombination of components within a cementitious or hydraulicallysettable composition that is an inorganic binder such as, for example,Portland cements, fly ash, and gypsums that harden and cure after beingexposed to water. These hydraulic cements develop increased mechanicalproperties such as hardness, compressive strength, tensile strength,flexural strength, and component surface bonds (e.g., binding ofaggregate to cement) by chemically reacting with water.

The terms “hydraulic paste” or “cement paste” are meant to refer to amixture of hydraulic cement and water in the green state as well ashardened paste that results from hydration of the hydraulic binder. Assuch, within a hydraulically settable composition, the cement pastebinds together the individual solid materials, such as fibers, cementparticles, aggregates, and the like.

The terms “fiber” and “fibers” include both natural and syntheticfibers. Fibers typically having an aspect ratio of at least about 10:1are added to an extrudable cementitious composition to increase theelongation, deflection, toughness, and fracture energy, as well asflexural and tensile strengths of the resulting extruded composite orfinished building product. Fibers reduce the likelihood that the greenextrudate, extruded products, and hardened or cured products producedtherefrom will rupture or break when forces are applied thereto duringhandling, processing, and curing. Also, fibers can absorb water andreduce the effective water/cement ratio.

The term “fiber-reinforced” is meant to refer to fiber-reinforcedcementitious compositions that include fibers so as to provide somestructural reinforcement to increase a mechanical property associatedwith a green extrudate, extruded products, and hardened or curedcomposites as well as the building products produced therefrom.Additionally, the key term is “reinforced,” which clearly distinguishesthe extrudable cementitious compositions, green extrudate, and curedbuilding products of the present disclosure from conventional settablecompositions and cementitious products. The fibers act primarily as areinforcing component to specifically add tensile strength, flexibility,and toughness to the building products as well as to reinforce anysurfaces cut or formed thereon. Because they are substantiallyhomogeneously dispersed, the building products do not separate ordelaminate when exposed to moisture as can products made using theconventional processes.

The term “mechanical property” is meant to include a property, variable,or parameter that is used to identify or characterize the mechanicalstrength of a substance, composition, or product of manufacture.Accordingly, a mechanical property can include the amount of elongation,deflection, or compression before rupture or breakage, stress and/orstrain before rupture, tensile strength, compressive strength, Young'sModulus, stiffness, hardness, deformation, resistance, and the like.

The terms “extrudate,” “extruded shape,” or “extruded product,” aremeant to include any known or future designed shape of products that areextruded using the extrudable cementitious compositions and methods ofthe present disclosure. For example, the extruded composite can beprepared into countertops, tiles, cladding, and roof tiles.Additionally, an extruded building product can initially be extruded asa “rough shape” and then shaped, ground, milled or otherwise refinedinto a product of manufacture, which is intended to be included by useof the present terms.

The term “extrusion” can include a process where a material is processedor pressed through an opening or through an area having a certain sizeso as to shape the material to conform with the opening or area. Assuch, an extruder pressing a material through a die opening can be oneform of extrusion. Alternatively, roller-extrusion, which includespressing a composition between a set of rollers, can be another form ofextrusion. Roller-extrusion is described in more detail below in FIG. 2.In general, extrusion refers to a process that is used to shape amoldable composition without cutting, milling, sawing or the like, andusually includes pressing or passing the material through an openinghaving a predefined cross-sectional area.

The terms “hydrated” or “cured” are meant to refer to a level of ahydraulic reaction which is sufficient to produce a hardenedcementitious building product having obtained a substantial amount ofits potential or maximum strength. Nevertheless, cementitious compositesor extruded building products may continue to hydrate or cure long afterthey have attained significant hardness and a substantial amount oftheir maximum strength.

The terms “green,” “green material,” “green extrudate,” or “green state”are meant to refer to the state of a cementitious composition which hasnot yet achieved a substantial amount of its final strength; however,the “green state” is meant to identify that the cementitious compositionhas enough cohesiveness to retain an extruded shape before beinghydrated or cured. As such, a freshly extruded extrudate comprised ofhydraulic cement and water should be considered to be “green” before asubstantial amount of hardening or curing has taken place. The greenstate is not necessarily a clear-cut line of demarcation as to theamount of curing or hardening that has taken place, but should beconstrued as being the state of the composition prior to beingsubstantially cured. Thus, a cementitious composition is in the greenstate post extrusion and prior to being substantially cured.

The term “form-stable” is meant to refer to the condition of a greenextrudate immediately upon extrusion which is characterized by theextrudate having a stable structure that does not deform under its ownweight. As such, a green extrudate that is form-stable can retain itsshape during handling and further processing.

The term “composite” is meant to refer to a form-stable composition thatis made up of distinct components such as fibers, rheology-modifiers,cement, aggregates, set accelerators, and the like. As such, a compositeis formed as the hardness or form-stability of the green extrudateincreases, and can be prepared into a building product.

The term “stone-like” or “stone-like properties” is meant to refer tocementitious compositions and extruded cementitious composite buildingproperties having a hardness value of at least 4 MOH, more suitably, atleast about 5 MOH, even more suitably a hardness of at least about 6MOH, and even more suitably a hardness of 7 to 8 MOH.

In one aspect, a cementitious composite product having stone-likeproperties is provided. The composite product includes an extrudablecementitious composition. The cementitious composite product has ahardness value of at least 4 MOH and a bulk density of at least 1.3g/cm³. More suitably, the cementitious composite product has a bulkdensity of from about 1.3 g/cm³ to about 2.3 g/cm³.

Extrudable Cementitious Compositions Used to Make the CementitiousComposite Product

The extrudable cementitious compositions used to make extrudedcementitious composite building products include water, hydrauliccement, fibers, aggregate, a rheology-modifying agent, and optionally, aset accelerator or a set retarder. In addition to these components, theextrudable cementitious compositions can be mixed with other admixturesto give an extruded cementitious composite product having the desiredproperties as described more fully below. More particularly, thecementitious composite products are formulated so as to have greaterhardness and compressive strength as compared to ordinary concrete, andhave greater toughness in order to better imitate the properties ofstone and solid surface materials. Furthermore, the cementitiouscomposite products of the present disclosure show flexibility, unlikeconventional stone products.

A. Hydraulic Cement, Water, and Aggregate

Hydraulic cements are materials that can set and harden in the presenceof water. The cement can be a Portland cement, modified Portland cement,or masonry cement. For purposes of this disclosure, Portland cementincludes all cementitious compositions which have a high content oftricalcium silicate, including Portland cement, cements that arechemically similar or analogous to Portland cement, and cements thatfall within ASTM specification C-150-00. Portland cement, as used in thetrade, means a hydraulic cement produced by pulverizing clinker,comprising hydraulic calcium silicates, calcium aluminates, and calciumaluminoferrites, and usually containing one or more forms of calciumsulfate as an interground addition. Portland cements are classified inASTM C 150 as Type I II, III, IV, and V. Other hydraulically settablematerials include ground granulated blast-furnace slag, hydraulichydrated lime, white cement, slag cement, calcium aluminate cement,silicate cement, phosphate cement, high-alumina cement, magnesiumoxychloride cement, oil well cements (e.g., Type VI, VII and VIII), andcombinations of these and other similar materials.

Pozzolanic materials such as slag, class F fly ash, class C fly ash andsilica fume can also be considered to be hydraulically settablematerials when used in combination with conventional hydraulic cements,such as Portland cement. A pozzolan is a siliceous or aluminosiliceousmaterial that possesses cementitious value and will, in the presence ofwater and in finely divided form, chemically react with calciumhydroxide produced during the hydration of Portland cement to formhydratable species with cementitious properties. Diatomaceous earth,opaline, cherts, clays, shales, fly ash, silica fume, volcanic tuffs,pumices, and trasses are some of the better known pozzolans. Certainground granulated blast-furnace slags and high calcium fly ashes possessboth pozzolanic and cementitious properties. Fly ash is defined in ASTMC618.

The amount of hydraulic cement and the pozzolanic material in theextrudable cementitious composition can vary depending on the identitiesand concentrations of the other components. In general, the combinedamount of hydraulic cement and pozzolanic material is in a range of fromabout 25% to about 75% by weight of the extrudable cementitiouscomposition, more suitably in a range of from about 35% to about 65% byweight of the extrudable cementitious composition, and most suitably ina range of from about 40% to about 60% by weight of the extrudablecementitious composition.

Briefly, within the extruded product, the hydraulic cement forms acement paste or gel by reacting with water, where the speed of thereaction can be greatly increased through the use of set accelerators orheat curing, and the strength and physical properties of thecementitious composite building products are modulated by a highconcentration of fibers. Usually, the amount of hydraulic cement in acured cementitious composite is described as a dry percentage (e.g., dryweight % or dry volume %). The amount of hydraulic cement can vary in arange from about 40% to about 95% by dry weight, more suitably about 50%to about 80% by dry weight, and most suitably about 60% to about 75% bydry weight. It should be recognized that some products can use more orless hydraulic cement, as needed and depending on other constituents.

The amount of water within the various compositions described herein canbe drastically varied over a large range. For example, the amount ofwater in the extrudable cementitious composition and green extrudate canrange from about 15% by weight extrudable cementitious composition toabout 75% by weight extrudable cementitious composition, more suitablyfrom about 35% to about 65%, and most suitably from about 40% to about60% by weight extrudable cementitious composition. On the other hand,the cured composite or hardened cementitious composite product can havefree water at less than 10% by weight, more suitably less than about 5%by weight, and most suitably less than about 2% water by weight;however, additional water can be bound with the rheology-modifier,fibers, or aggregates.

The amount of water in the extrudate during the rapid reaction periodshould be sufficient for curing or hydrating so as to provide thefinished properties described herein. Nevertheless, maintaining arelatively low water to cement ratio (i.e., w/c) increases the strengthof the final cementitious composite products. Accordingly, the actual ornominal water to cement ratio will typically initially range from about0.1 to about 0.6.

While it is desirable for the cementitious composite building productsto have properties similar to those of stone, it has been discoveredthat the cementitious building products prepared using the methods ofthe present disclosure have lower densities as compared to natural stoneand solid surface products. More particularly, the cementitiouscomposite building products have a density of at least about 1.3 g/cm³and less than 3.0 g/cm³, more suitably, at least about 1.3 g/cm³ andless than about 2.3 g/cm³, and even more suitably, from about 1.6 g/cm³to about 1.7 g/cm³, and even.

Aggregates are also included in the extrudable cementitious compositionto provide hardness to the cementitious composite products. Moreparticularly, stronger, harder aggregates are typically included asthese aggregates will deteriorate the paste strength of the cementitiouscomposite products less than in conventional products.

The aggregate includes both fine aggregate and coarse aggregate.Examples of suitable materials for coarse and/or fine aggregates includesilica, quartz, crushed round marble, glass spheres, granite, limestone,bauxite, calcite, feldspar, alluvial sands, or any other durableaggregate, and mixtures thereof. In a preferred embodiment, the fineaggregate consists essentially of “sand” and the coarse aggregateconsists essentially of “rock” (e.g., ⅜ inch and/or ¾ inch rock) asthose terms are understood by those of skill in the art.

In one aspect, the extrudable cementitious composition (and thecementitious composite product) includes two separate sizes of coarseaggregate (i.e., more coarse and less coarse aggregates). Moreparticularly, the extrudable cementitious composition can include morecoarse aggregate such as ¾ inch rock and less coarse aggregate such as ⅜inch rock.

It should be recognized, that while discussed herein as using two sizesof coarse aggregate, the extrudable cementitious composition may beproduced with either solely the less coarse or solely the more coarseaggregate without departing from the present disclosure.

B. Fibers

The extrudable cementitious composition and extruded cementitiouscomposite building products include a relatively high concentration offibers compared to conventional concrete compositions. Moreover, thefibers are typically substantially homogeneously dispersed throughoutthe cementitious composition in order to maximize the beneficialproperties imparted by the fibers. The fibers are present in order toprovide structural reinforcement to the extrudable cementitiouscomposition, green extrudate, and the cementitious composite buildingproduct.

Various types of fibers may be used in order to obtain specificcharacteristics. For example, the extrudable cementitious compositionscan include naturally occurring organic fibers extracted from hemp,cotton, plant leaves or stems, hardwoods, softwoods, or the like, fibersmade from organic polymers, examples of which include polyester nylon(i.e., polyamide), polyvinyl alcohol (PVA), polyethylene, andpolypropylene, and/or inorganic fibers, examples of which include glass,graphite, silica, silicates, microglass made alkali resistant usingborax, ceramics, carbon fibers, carbides, metal materials, and the like.Particularly preferred fibers, for example, include glass fibers,woolastanite, abaca, bagasse, wood fibers (e.g., soft pine, southernpine, fir, and eucalyptus), cotton, silica nitride, silica carbide,silica nitride, tungsten carbide, and Kevlar; however, other types offibers can be used.

The fibers used in making the cementitious compositions can have a highlength to width ratio (or “aspect ratio”) because longer, narrowerfibers typically impart more strength per unit weight to the finishedcementitious composite building product. The fibers can have an averageaspect ratio of at least about 10:1, preferably at least about 50:1,more preferably at least about 100:1, and most preferably greater thanabout 200:1.

In one embodiment, the fibers can be used in various lengths such as,for example, from about 0.1 cm to about 2.5 cm, more preferably fromabout 0.2 cm to about 2 cm, and most preferably about 0.3 cm to about1.5 cm. In one embodiment, the fibers can be used in lengths less thanabout 5 mm, more preferably less than about 1.5 mm, and most preferablyless than about 1 mm.

In one embodiment, very long or continuous fibers can be admixed intothe cementitious compositions. As used herein, a “long fiber” is meantto refer to a thin long synthetic fiber that is longer than about 2.5cm. As such, a long fiber can be present with lengths ranging from about2.5 cm to about 10 cm, more preferably about 3 cm to about 8 cm, andmost preferably from about 4 cm to about 5 cm.

The concentration of fibers within the extrudable cementitiouscompositions can vary widely in order to provide various properties tothe extruded composition and the finished cementitious compositeproduct. Generally, the fibers can be present in the extrudablecomposition in an amount of greater than about 1% by volume ofextrudable cementitious composition, more suitably greater than about2%, and more suitably greater than about 3%, and even more suitably fromabout 3% to about 20%, and most suitably from about 3.5% to about 8% byvolume extrudable cementitious composition.

Additionally, specific types of fibers can vary in amount in thecompositions. For example, in one embodiment, PVA can be present in theextrudable cementitious composition in an amount of from about 1.5% toabout 3.5% by volume extrudable cementitious composition. Soft and/orwoods, such as cellulose fibers, can be present in the extrudablecementitious composition in amounts described above with respect togeneral fibers or present in an amount of from about 1.5% to about 5.0%by volume extrudable cementitious composition.

In one embodiment, the type of fiber can be selected based on thedesired structural features of the finished product comprised of thecementitious composite product, where it can be preferred to have densesynthetic fibers compared to light natural fibers or vice versa.Typically, the specific gravity of natural or softwood fibers is about1.2. On the other hand, synthetic fibers can have specific gravitiesthat range from about 1 for polyurethane fibers, about 1.3 for PVAfibers, about 1.5 for Kevlar fibers, about 2 for graphite and quartzglass, about 2.3 for glass fibers, about 3.2 for silicon carbide andsilicon nitride, about 7 to about 9 for most metals with about 8 forstainless steel fibers, about 5.7 for zirconia fibers, to about 15 fortungsten carbide fibers. As such, natural fibers tend to have densitiesof about 1 or less, and synthetic fibers tend to have densities of fromabout 1 to about 15.

In one embodiment, a mixture of regular or long length fibers, such aspine, fir, or other natural fibers, may be combined with micro-fibers,such as woolastinite or micro glass fibers, to provide uniqueproperties, including increased toughness, flexibility, and flexuralstrength, with the larger and smaller fibers acting on different levelswithin the cementitious composition.

In view of the foregoing, the fibers are added in relatively highamounts in order to yield a cementitious composite building producthaving increased tensile strength, elongation, deflection,deformability, and flexibility. The fibers contribute to the ability ofthe cementitious composite building product to be sawed, screwed,ground, and/or milled like stone.

C. Rheology Modifying Agent

In one or more embodiments of the present disclosure, the extrudablecementitious compositions and the cementitious composite buildingproducts include a rheology-modifying agent (“rheology-modifier”). Therheology-modifier can be mixed with water and fibers to aid insubstantially uniformly (or homogeneously) distributing the fiberswithin the cementitious composition. Additionally, the rheology-modifiercan impart form-stability to an extrudate. In part, this is because therheology-modifier acts as a binder when the composition is in a greenstate to increase early green strength so that it can be handled orotherwise processed without the use of molds or other shape-retainingdevices. The rheology-modifying agent helps control porosity (i.e.,yields uniformly dispersed pores when water is removed by evaporation).Further, the rheology-modifying agent can impart increased toughness andflexibility to a cured cementitious composite product which can resultin enhanced deflection characteristics. Thus, the rheology-modifiercooperates with other compositional components in order to achieve amore deformable, flexible, bendable, compactable, tough, and/or elasticcementitious building product.

For example, variations in the type, molecular weight, degree ofbranching, amount, and distribution of the rheology-modifier can affectthe properties of the extrudable cementitious composition, greenextrudate, and cementitious composite building products. As such, thetype of rheology-modifier can be any polysaccharide, proteinaceousmaterial, and/or synthetic organic material that is capable of being orproviding the rheological properties described herein. Examples of somesuitable polysaccharides, particularly cellulosic ethers, includemethylhydroxyethylcellulose, hydroxymethylethylcellulose,carboxymethylcellulose, methylcellulose, ethylcellulose,hydroxyethylcellulose, and hydroxyethylpropylcellulose, starches such asamylopectin, amylose, starch acetates, starch hydroxyethyl ethers, ionicstarches, long-chain alkylstarches, dextrins, amine starches, phosphatestarches, and dialdehyde starches, polysaccharide gums such as seagel,alginic acid, phycocolloids, agar, gum arabic, guar gum, locust beangum, gum karaya, gum tragacanth, and the like. Examples of someproteinaceous materials include collagens, caseins, biopolymers,biopolyesters, and the like. Examples of synthetic organic materialsthat can impart rheology-modifying properties include petroleum-basedpolymers (e.g., polyethylene, polypropylene), latexes (e.g.,styrene-butadiene), and biodegradable polymers (e.g., aliphaticpolyesters, polyhydroxyalkanoates, polylactic acid, polycaprolactone),polyvinyl chloride, polyvinyl alcohol, and polyvinyl acetate. Clay canalso act as a rheology-modifier to aid in dispersing the fibers and/orimparting form stability to the green extruded intermediate.

The amount of rheology-modifier within the extrudable cementitiouscomposition and cementitious building product can vary from low to highconcentrations depending on the type, branching, molecular weight,and/or interactions with other compositional components. For example,the amount of rheology-modifier present in the extrudable cementitiouscompositions can range from about 0.1% to about 4% by volume ofextrudable cementitious compositions, suitably from about 0.25% to about2% by volume, even more suitably about 0.5% to about 1.5% by volume, andmost suitably from about 0.75% to about 1% by volume of extrudablecementitious compositions. The amount of rheology-modifier present inthe cured cementitious composite products can range from about 0.5% toabout 1% by volume.

Additionally, examples of synthetic organic materials, which areplasticizers usually used along with the rheology-modifier, includepolyvinyl pyrrolidones, polyethylene glycols, polyvinyl alcohols,polyvinylmethyl ethers, polyacrylic acids, polyacrylic acid salts,polyvinylacrylic acids, polyvinylacrylic acid salts, polyacrylimides,ethylene oxide polymers, polylactic acid, synthetic clay,styrene-butadiene copolymers, latex, copolymers thereof, mixturesthereof, and the like. For example, the amount of plasticizers in theextrudable cementitious composition can range from no plasticizer toabout 40% plasticizer by weight, more suitably about 1% to about 35%plasticizer by weight, even more suitably from about 2% to about 30%,and most suitably from about 5% to about 25% by weight.

D. Filler

In one embodiment, the extrudable composition, green intermediateextrudate, and cured cementitious composite product can include fillers.Alternatively, there are instances where filler materials arespecifically excluded. Fillers, if used at all, are generally includedin smaller amounts and mainly to decrease the cost of the extrudedproducts. Because it is desired to obtain extruded products in the formof stone-like building material having the properties of stone, fillersshould be selected that do not yield a product that is too soft ordifficult to work with. Examples, of fillers include hard silicate,glass, basalt, granite, calcined bauxite. Additional informationregarding the types and amounts of fillers that can be used in thecementitious compositions are known to one of ordinary skill in the art.Fillers can further be chosen to add artistic or aesthetic properties tothe cementitious composite products.

In one embodiment, the extrudable cementitious compositions can includea widely varying amount of fillers. Specifically, when used, fillers caneach independently be present at less than about 10% by weight ofextrudable cementitious composition, suitably less than about 7% byweight, more suitably less than about 3% by weight, and most suitablybetween about 2% to about 12% by weight of extrudable cementitiouscomposition.

In one embodiment, the cured cementitious composite products can includea widely varying amount of fillers. Specifically, when used, fillers caneach independently be present at less than about 15% by weight, suitablyless than about 10% by weight, more suitably less than about 5% byweight, and most suitably between about 3% to about 15% by weight. Insome instances, fillers such as limestone can be present up to about 70%by weight. For example, when included in a cured cementitious composite,vermiculite can be present from about 2% by weight to about 20% byweight, and suitably from about 3% by weight to about 16% by weight.

E. Admixtures and Other Materials

A wide variety of admixtures and other materials can be added to theextrudable cementitious compositions to give the extrudable cementitiouscompositions and cementitious composite products made therefrom desiredproperties. Examples of admixtures that can be used in the extrudablecementitious compositions of the disclosure include, but are not limitedto, set accelerators, air entraining agents, strength enhancing aminesand other strengtheners, dispersants, water reducers, superplasticizers,water binding agents, viscosity modifiers, corrosion inhibitors,pigments, wetting agents, water soluble polymers, water repellents,permeability reducers, pumping aids, fungicidal admixtures, germicidaladmixtures, insecticidal admixtures, finely divided mineral admixtures,alkali reactivity reducers, bonding admixtures, nucleating agents,volatile solvents, salts, buffering agents, acidic agents, coloringagents, and the like, and mixtures thereof.

A set accelerator can be included in the extrudable cementitiouscomposition, green intermediate extrudate, and cementitious compositebuilding product. As described herein, the set accelerator can beincluded so as to decrease the duration of the induction period orhasten the onset of the rapid reaction period. Accordingly, traditionalset accelerators such as MgCl₂, NaCO₃, KCO₃ CaCl₂ and the like can beused, but may result in a decrease in the compressive strength of thecementitious composite building product; however, this may be adesirable by-product in order to yield a product that can be sawed,nailed, ground, and milled like stone. For example, the traditional setaccelerators can be present in the green intermediate extrudate fromabout 0.001% to about 5% by total weight, more suitably from about 0.05%to about 2.5% by weight, and most suitably from about 0.11% to about 1%by weight.

Retarding agents, also known as retarders, set retarders,delayed-setting or hydration control admixtures, may also optionally beused to retard, delay, or slow the rate of cement hydration.Furthermore, retarding agents can maintain constant rheology and reducebuildup in the extruder. They can be added to the extrudablecomposition, green extrudate, and cementitious composite buildingproduct. Examples of retarding agents include lignosulfonates and saltsthereof, hydroxylated carboxylic acids, borax, gluconic acid, tartaricacid, mucic acid, and other organic acids and their corresponding salts,phosphonates, monosaccharides, disaccharides, trisaccharides,polysaccharides, certain other carbohydrates such as sugars andsugar-acids, starch and derivatives thereof, cellulose and derivativesthereof, water-soluble salts of boric acid, water-soluble siliconecompounds, sugar-acids, and mixtures thereof. Exemplary retarding agentsare commercially available under the tradename Delvo®, fromMasterbuilders (a division of BASF, The Chemical Company, Cleveland,Ohio).

Air-entraining agents are compounds that entrain microscopic air bubblesin cementitious compositions, which then harden into cementitiouscomposite products having microscopic air voids. Entrained airdramatically improves the durability of product exposed to moistureduring freeze thaw cycles. Air-entraining agents can also reduce thesurface tension of an extrudable cementitious composition at lowconcentration. Air entrainment can also increase the workability ofextrudable cementitious compositions and reduce segregation andbleeding. Examples of suitable air-entraining agents include wood resin,sulfonated lignin, petroleum acids, proteinaceous material, fatty acids,resinous acids, alkylbenzene sulfonates, sulfonated hydrocarbons, vinsolresin, anionic surfactants, cationic surfactants, nonionic surfactants,natural rosin, synthetic rosin, inorganic air entrainers, syntheticdetergents, the corresponding salts of these compounds, and mixtures ofthese compounds. Air-entraining agents are added in an amount to yield adesired level of air in an extrudable cementitious composition.

In another alternative embodiment, the concrete composition does notinclude any air entraining agent but rather a greater quantity ofsuperplasticizer, as discussed below.

Strength enhancing amines are compounds that improve the compressivestrength of cementitious composite products made from extrudablecementitious compositions. The strength enhancing amine includes one ormore compounds from the group selected frompoly(hydroxyalkylated)polyethyleneamines,poly(hydroxyalkylated)poly-ethylenepolyamines,poly(hydroxyalkylated)polyethyleneimines,poly(hydroxyl-alkylated)polyamines, hydrazines, 1,2-diaminopropane,polyglycoldiamine, poly-(hydroxylalkyl)amines, and mixtures thereof. Anexemplary strength enhancing amine is 2,2,2,2tetra-hydroxydiethylenediamine.

Dispersants are used in extrudable cementitious compositions to increaseflowability without adding water. Dispersants can be used to lower thewater content in the extrudable cementitious composition to increasestrength without adding additional water. A dispersant, if used, can beany suitable dispersant such as lignosulfonates, beta naphthalenesulfonates, sulfonated melamine formaldehyde condensates,polyaspartates, polycarboxylates with and without polyether units,naphthalene sulfonate formaldehyde condensate resins, or oligomericdispersants. Depending on the type of dispersant, the dispersant mayfunction as a plasticizer, high range water reducer, fluidizer,antiflocculating agent, and/or superplasticizer.

One class of dispersants includes mid-range water reducers. Mid-rangewater reducers should at least meet the requirements for Type A in ASTMC 494.

Another class of dispersants includes high range water-reducers (HRWR).These dispersants are capable of reducing water content of a givenextrudable cementitious composition by as much as from about 10% toabout 50%. HRWRs can be used to increase strength or to greatly increasethe slump to produce a “flowing” extrudable cementitious compositionwithout adding additional water. HRWRs that can be used in the presentdisclosure include those covered by ASTM C 494 and types F and G, andTypes 1 and 2 in ASTM C 1017. Examples of HRWRS are described in U.S.Pat. No. 6,858,074, which is hereby incorporated by reference to theextent that it is consistent herewith.

Dampproofing admixtures reduce the permeability of extrudablecementitious composition that have low cement contents, highwater-cement ratios, or a deficiency of fines in the aggregate. Theseadmixtures retard moisture penetration into dry concrete and includecertain soaps, stearates, and petroleum products.

Permeability reducers are used to reduce the rate at which water underpressure is transmitted through the extrudable cementitious composition(and the cementitious composite products). Silica fume, fly ash, groundslag, natural pozzolans, water reducers, and latex can be employed todecrease the permeability of the extrudable cementitious composition.

Shrinkage reducing agents include but are not limited to alkali metalsulfate, alkaline earth metal sulfates, alkaline earth oxides, e.g.,sodium sulfate and calcium oxide.

Finely divided mineral admixtures are materials in powder or pulverizedform added to extrudable cementitious compositions before or during themixing process to improve or change some of the plastic or hardenedproperties of Portland cement. The finely divided mineral admixtures canbe classified according to their chemical or physical properties as:cementitious materials; pozzolans; pozzolanic and cementitiousmaterials; and nominally inert materials. Nominally inert materialsinclude finely divided raw quartz, dolomites, limestones, marble,granite, and others.

Natural and synthetic admixtures are used to color extrudablecementitious composition for aesthetic and safety reasons. Coloringadmixtures are usually composed of pigments and include carbon black,iron oxide, phthalocyanine, umber, chromium oxide, titanium oxide andcobalt blue.

In one embodiment, a substantially cured cementitious composite productthat is reinforced with fibers can be coated with a protective orsealing material such as a paint, stain, varnish, texturizing coating,and the like. As such, the coating can be applied to the cementitiouscomposite building product after it is substantially cured. For example,the cementitious building product can be stained so that the fiberspresent on the surface are a different shade from rest of the product,and/or texturized so as to resemble a stone product.

Sealants known in the concrete industry can be applied to the surfaceand/or incorporated into the cementitious composition in order toprovide waterproofing properties. These include silanes and siloxanes.

Manufacturing Cementitious Composite Products

FIG. 1 is a schematic diagram that illustrates an embodiment of amanufacturing system and equipment that can be used during the formationof an extrudable cementitious composition, green intermediate extrudate,cementitious composite product, and/or cementitious composite buildingproduct. It should be recognized that this is only one exampleillustrated for the purpose of describing a general processing systemand equipment, where various additions and modifications can be madethereto in order to prepare the cementitious composite products (andbuilding products). Also, the schematic representation should not beconstrued in any limiting manner as to the presence, arrangement, shape,orientation, or size of any of the features described in connectiontherewith. With that said, a more detailed description of the system andequipment that can prepare the extrudable cementitious compositions aswell as cementitious composite building products that are in accordancewith the present disclosure is provided.

Referring now to FIG. 1A, an embodiment of an extrusion system 10 inaccordance with the present disclosure is provided. Such an extrusionsystem 10 includes a first mixer 16, optional second mixer 18, and anextruder 24. The first mixer 16 is configured to receive at least onefeed of materials through at least a first feed stream 12 for beingmixed into a first mixture 20 (for example, in one embodiment the firstmixture 20 is the fibrous mixture described above). After adequatemixing, which can be performed under high shear, while maintaining atemperature below that which accelerates hydration, the first mixture 20is removed from the first mixer 16 as flow of material ready for furtherprocessing.

By mixing the first mixture 20 apart from any additional components, therespective mixed components can be homogeneously distributed throughoutthe composition. For example, it can be advantageous to homogeneouslymix the fibers with at least the rheology modifier and water beforecombining them with the additional components. As such, therheology-modifier, fibers, and/or water are mixed under high shear so asto increase the homogeneous distribution of fibers therein. The rheologymodifying agent and water form a plastic composition having high yieldstress and viscosity that is able to transfer the shearing forces fromthe mixer down to the fiber level. In this way, the fibers can behomogeneously dispersed throughout the fibrous mixture using much lesswater than required in conventional procedures, which typically requireup to 99% water to disperse the fibers.

The optional second mixer 18 has a second feed stream 14 that suppliesthe material to be mixed into a second mixture 22, where such mixing canbe enhanced by the inclusion of a heating element. For example, thesecond mixer 18 can receive and mix the additional components, such asthe additional water, set accelerators, hydraulic cement, plasticizers,aggregates, nucleating agents, dispersants, polymeric binders, volatilesolvents, salts, buffering agents, acidic agents, coloring agents,fillers, and the like before combining them with other components toform the extrudable cementitious composition. The second mixer 18 isoptional because the additional components could be mixed with thefibrous mixture in the first mixer 16.

As in the illustrated schematic diagram, the extruder 24 includes anextruder screw 26, optional heating elements (not shown), and a die head28 with a die opening 30. Optionally, the extruder can be a singlescrew, twin screw, and/or a piston-type extruder. After the firstmixture 20 and second mixture 22 enter the extruder they can be combinedand mixed into an extrudable cementitious composition.

By mixing the components, an interface is created between the differentcomponents, such as the rheology-modifying agent and fibers, whichallows for individual fibers to pull apart from each other. Byincreasing the viscosity and yield stress with the rheology-modifyingagent, more fibers can be substantially homogenously distributedthroughout the mixture and final cured product. Also, the cohesionbetween the different components can be increased so as to increaseinter-particle and capillary forces for enhanced mixing andform-stability after extrusion. For example, the cohesion between thedifferent components can be likened to clay so that the green extrudatecan be placed on a pottery wheel and worked similar to common clays thatare fabricated into pottery.

In one embodiment, additional feed streams (not shown) can be located atany position along the length of the extruder 24. The availability ofadditional feed streams can enable the manufacturing process to addcertain components at any position so as to modify the characteristicsof the extrudable cementitious composition during mixing and extrudingas well as the characteristics of the green intermediate extrudate afterextrusion. For example, in one embodiment it can be advantageous tosupply the set accelerator into the composition within about 60 minutesto within about 1 second before being extruded. More preferably, the setaccelerator is mixed into the composition within about 45 minutes toabout 5 seconds before being extruded, even more suitably within about30 minutes to about 8 seconds, and most suitably within about 20 minutesto about 10 seconds before being extruded. This can enable the greenintermediate extrudate to be configured for increased form-stability anda shortened induction period before the onset of the rapid reactionperiod.

With continuing reference to FIG. 1A, as the extrudable cementitiouscomposition moves to the end of the extruder 24, it passes through thedie head 28 before being extruded at the die opening 30. The die head 28and die opening 30 can be configured into any shape or arrangement solong as to produce a green intermediate extrudate (also referred toherein as green extrudate or extrudate) that is capable of being furtherprocessed or finished into a cementitious composite building product. Inthe illustrated embodiment, it can be advantageous for the die opening30 to have a circular diameter so that the extrudate 32 has a rod-likeshape. Other exemplary cross-sectional shapes are illustrated in FIG.1C, including hexagonal 42, rectangular 44, square 46, or I-beam 48. Theextruded products can be characterized as being immediately form-stablewhile in the green state. That is, the extrudate can be immediatelyprocessed without deforming, wherein the processing can include cutting,sawing, shaping, grinding, milling, forming, drilling, and the like. Assuch, the extrudate in the green state does not need to be cured beforebeing prepared into the size, shape, or form of the finishedcementitious composite building product. For example, the green-stateprocessing can include the following: (a) creating stone-like surfaces,by milling, sawing, cutting, grinding or the like, that have specifieddimensions, such as width, thickness, length, radius, diameter, surfacetexture, and the like; (b) bending the extrudate so as to form a curvedcementitious product, which can be of any size and shape, such as, acurved countertop or edge, and other ornamental and/or structuralmembers; (c) creating products having lengths of 6 ft 9 in, 8 ft 8 in, 9ft 1 in, 27 ft, 40 if, 41 ft, 60 if, 61 ft, 80 ft, 81 ft, and the like;(d) texturizing with rollers, which can impart stone and or marble-likesurfaces to the cementitious composite building product; (e) having thesurface painted, waterproofed, or otherwise coated, which can applycoatings comprised of silanes, siloxanes, latex, and the like; and (l)transported, shipped, or otherwise moved and/or handled. Also, thebyproducts that are produced from the green-state processing can beplaced into the feed compositions and reprocessed. Thus, the greencementitious byproducts can be recycled, which can significantly reducewaste and manufacturing costs.

FIG. 1B is a schematic diagram of a die head 29 that can be used withthe extrusion process of FIG. 1A. As such, the die head 29 includes adie opening 30 that has a hole forming member 31. The hole formingmember 31 can be circular as shown, or have any cross-sectional shape.As such, the hole forming member 31 can form a hole in the extrudate,which is depicted in FIG. 1C. Since the extrudate can be form-stableimmediately upon extrusion, the hole can retain the size and shape ofthe hole forming member 31. Additionally, various die heads having holeforming members that can produce annular extrudates are well known inthe art and can be adapted or modified, if needed, to be usable with theextrusion processes in accordance with the present disclosure.

With reference now to FIG. 1C, additional embodiments of extrudates 40are depicted. Accordingly, the die head and die opening of FIG. 1A or 1Bcan be modified or altered so as to provide extrudates 40 having variouscross-sectional areas, where the extrudate 40 cross-sectional area canbe substantially the same as the cross-sectional area of the dieopening. For example, the cross-sectional area can be a hexagon 42,rectangle 44 (e.g., two-by-four, one-by-ten, etc.), square 46, I-beam48, or a cylinder 50, optionally having a continuous hole 49. Also,additional cross-sectional shapes can be prepared via extrusion. Moreparticularly, the die head and die opening of FIG. 1B can be used sothat the hexagon 42, rectangle 44, square 46, I-beam 48, or cylinder 50can optionally include continuous circular holes 51, rectangular holes53, square holes 57, or the like. Also, complex dies heads and openingscan be used for preparing the cylinder 50 having the continuous hole 49and a plurality of smaller holes 51. Moreover, any generalcross-sectional shape can be further processed into a specific shapesuch as, for example, a two-by-four from a four-by-four square shape.Alternatively, the die orifice may yield oversized products that arelater trimmed to the desired specifications in order to ensure greateruniformity.

Accordingly, the foregoing processes can be usable for extrudingbuilding products with one or more continuous holes to reduce weight ofthe products. For example, a countertop-like material can be extrudedhaving one or more holes into which rebar can be inserted, either whilein a green state or after curing. In the case of a cured countertopmaterial, the rebar may be held in place within the hole using epoxy orother adhesive to provide strong bonding between the rebar and material.For example, the cylinder 50 of FIG. 1C, as well as the other shapes,can be fabricated into large countertops. These structures canoptionally include a large interior opening 49 to reduce the mass andcost, along with smaller holes 51 in the wall to permit the insertion ofstrengthening rebar, as shown.

In one embodiment, the extrudable cementitious composition is de-airedbefore being extruded. While some processes can employ a specificde-airing process to remove a substantial amount of air from theextrudable cementitious composition, other processes can remove the airby the mixing process that occurs in the extruder. In any event, theactive or passive de-airing can provide an extrudate that does not havelarge air voids or cellular formations. In general, it is preferable tode-air the extrudable cementitious composition as this decreases theporosity of the composition, and thus, increases the strength of thefinal product. For example, a de-aired cementitious composite can haveentrapped air in an amount of from about 0% to about 10%, more suitablyfrom about 0.1% to about 5%, and most suitably about 0.2% to about 3%.Thus, the extrudate and resulting cementitious composite buildingproduct can be fabricated so as to be substantially or completely devoidof any multi-cellular formations.

In one embodiment, the extrudate can be further processed in a dryer orautoclave. The dryer can be useful for drying the extrudate so as toremove excess water from the hardened product. In another embodiment,the extrudate can be processed through an autoclave in order to increasethe rate of curing and strength development to produce an increase instrength of the product of from about 50% to about 100%.

FIG. 2 is a schematic diagram depicting an alternative extrusion processthat can be used to prepare the cementitious composite building productsin accordance with the present disclosure. As such, the extrusionprocess can be considered to use a roller-extrusion system 200 that usesrollers to extrude the extrudable cementitious composition into a greenintermediate extrudate. Such a roller extrusion system 200 includes amixer 216 configured to receive at least one feed of materials through afeed stream 212 for being mixed into a mixture 220. After adequatemixing, which can be performed as described herein, the mixture 220 isremoved from the mixer 216 as flow of material ready for furtherprocessing.

The mixture 220 is then applied to a conveyor 222 or other similartransporter so as to move the extrudable cementitious composition fromthe site of application. This allows the composition to be formed into acementitious flow 224 that can be processed. As such, the cementitiousflow 224 can be passed under a first roller 226 that is set at apredefined distance from the conveyor 222 and having a predefinedcross-sectional area with respect thereto, which can press or shape thecementitious flow 224 into a green intermediate extrudate 228.Optionally, the conveyor 222 can then deliver the green intermediateextrudate 228 through a first calender 230 comprised of an upper roller230 a and a lower roller 230 b. The calender 230 can be configured tohave a predefined cross-sectional area so that the green intermediateextrudate 228 is further shaped and/or compressed into a shaped greenintermediate extrudate 242. Also, an optional second calender 240comprised of a first roller 240 a and a second roller 240 b can be usedin place of the first calender 230 or in addition thereto. A combinationof calenders 230, 240 can be favorable for providing a greenintermediate extrudate that is substantially shaped as desired.Alternatively, the first roller 226 can be excluded and the cementitiousflow 224 can be processed through any number of calenders 230, 240.

Additionally, the shaped green intermediate extrudate 242, or otherextrudate described here, such as from the process illustrated in FIG.1A, can be further processed by a processing apparatus 244. Theprocessing apparatus 244 can be any type of equipment or system that isemployed to process the green intermediate extrudate materials asdescribed herein. As such, the processing apparatus 244 can saw, grind,mill, cut, bend, coat, dry or otherwise shape or further process theshaped green intermediate extrudate 242 into a processed extrudate 246.Also, the byproduct 260 obtained from the processing apparatus 244 canbe recycled into the feed composition 212, or applied to the conveyor222 along with the mixture 220.

In one embodiment, a combined curing/drying process can be used to cureand dry the hydraulic cement to form the extruded cementitiouscomposite. For example, the combined curing/drying process can beperformed at a temperature of from about 75-95° C. for 48 hours in orderto obtain about 80% of the final strength. However, larger blocks cantake additional time in any curing and/or drying process. In anotherembodiment, the combined curing/drying process can be conducted in anautoclave. For example, the autoclave can cure/dry at a temperature ofabout 190° C., at about 12 bars, for about 12 hours.

Optionally, the extrudate can be covered in plastic and/or stored for aperiod of time to allow the extrudate to cure. This can allow theextrudate to harden over time in order to produce the requisite strengthfor the cured cementitious composite product. For example, after 28days, the cured cementitious composite product can have about 80% offinal strength, and can be placed in a dryer to remove residual water.

In another embodiment, combined steam curing and autoclaving processesare used to cure the hydraulic cement. Typically, the cement isinitially steam cured for about 1 to about 6 hours and is thenautoclaved at temperatures of about 190° C. or greater at 12 bars forapproximately 12 hours. By autoclaving, the resulting cementitiousproduct obtains about 100% of additional strength.

In one embodiment, the green intermediate extrudate can be furtherprocessed by causing or allowing the hydraulic cement within the greenintermediate extrudate to hydrate or otherwise cure so as to form asolidified cementitious composite building product. As such, thecementitious composite building product can be prepared so as to beimmediately form-stable after being extruded so as to permit thehandling thereof without breakage. More preferably, the extrudablecementitious composition, or green intermediate extrudate can beform-stable within minutes, more suitably within 10 minutes, even moresuitably within 5 minutes, and most suitably within 1 minute after beingextruded. The most optimized and preferred composition and processingcan result in a green intermediate extrudate that is form-stable uponextrusion. The use of a rheology-modifying agent can be used to yieldextrudates that are immediately form-stable even in the absence ofhydration of the hydraulic cement binder.

In order to achieve form-stability, the manufacturing process can eithersimply allow the green intermediate extrudate to sit and set without anyadditional processing or it can be caused to hydrate and/or set. Whenthe manufacturing includes causing the green intermediate extrudate tohydrate, set or otherwise cure, the manufacturing system can include adryer, heater or autoclave. The dryer or heater can be configured togenerate enough heat to drive off or evaporate the water from theextrudate so as to increase its rigidity and porosity or induce theonset of the rapid reaction period. On the other hand, an autoclave canprovide pressurized steam to induce the onset of the rapid reactionperiod.

In one embodiment, the green intermediate extrudate can be allowed orinduced to initiate the rapid reaction period as described herein inaddition to including a set accelerator within the extrudablecementitious composition. As such, the green intermediate extrudate canbe induced to initiate the rapid reaction period by altering thetemperature of the extrudate or changing the pressure and/or relativehumidity. Also, the rapid reaction period can be induced by configuringthe set accelerator to initiate the reactions within a predeterminedperiod of time after being extruded.

In one embodiment, the preparation of a cementitious composite orcementitious composite building product can include substantiallyhydrating or otherwise curing the green intermediate extrudate into thecementitious composite building product within a shortened period, or afaster reaction rate, compared to conventional concretes or otherhydraulically settable materials. As a result, the cementitiouscomposite building product can be substantially cured or hardened,depending on the type of binder that is used, within about 48 hours,more suitably within about 24 hours, even more suitably within 12 hours,and most suitably within 6 hours. Thus, the manufacturing system andprocess can be configured in order to obtain fast cure rates so that thecementitious composite building product can be further processed orfinished.

In one embodiment, a curing or cured cementitious composite can befurther processed or finished. Such processing can include sanding,cutting, drilling, grinding, milling and/or shaping the cementitiouscomposite product into a desired shape, wherein the composition lends tosuch shaping. Accordingly, when a cementitious composite buildingproduct is cut, the fibers and rheology-modifier can contribute to thestraight cut-lines that can be formed without cracking or chipping thecut surface or internal aspects of the material. This enables thecementitious composite building product to be a stone substitute becausea larger slab of material can be purchased by a consumer and cut withstandard equipment into the desired shapes and lengths.

In one embodiment, the form-stable green intermediate extrudate can beprocessed through a system that modifies the external surface of theproduct. One example of such a modification is to pass the greenintermediate extrudate through a calender or series of rollers that canimpart a stone-like appearance. As such, the cementitious compositebuilding product can be a stone substitute having the aestheticappearance and texture of stone or other solid surface material. Also,certain colorants, dyes, and/or pigments can be applied to the surfaceor dispersed within the cementitious composite building product so as toachieve the color of various types of stones.

The green extruded intermediates can also be reshaped while in a greenstate to yield, for example, curved products or other building productshaving a desired radius. This is a significant advantage overtraditional stone products, which are difficult to curve and/or whichmust be ground and/or milled to have a curved profile. In oneembodiment, the cementitious composite building product can be sandedand/or buffed in a manner that exposes the fibers at the surface. Due tothe high percentage of fiber in the product, a large number of fiberscan be exposed at the surface. This can provide for interesting andcreative textures that can increase the aesthetic qualities of theproduct.

Cementitious Composite Building Products

The present disclosure provides the ability to manufacture cementitiouscomposite building products having virtually any desired size and shape,whether extruded in the desired shape or later cut, ground, milled orotherwise formed into the desired size and shape. Examples includearchitectural products such as countertops, tiles, cladding, roof tiles,and the like, as well as structural products such as pre-cast orpre-formed members with extrusion or injected molded products.Accordingly, the cementitious composite building product can be loadbearing or non-load bearing. Thus, the cementitious composite buildingproduct can be used as a stone substitute for almost any buildingapplication.

The cured cementitious composite product can be configured to havevarious properties in order to function as a stone substitute. Anexample of a cured cementitious composite product that can function as astone substitute can have any of the following properties: have ahardness and/or toughness similar to stone and other solid surfacematerials such to prevent cracking and splitting of the product; havinga high compressive strength to allow for support and durability for usein stone-like products; and high flexural strength to allow forflexibility for use in manipulating the product and/or bending andcurving the product into a desired product shape. These properties areachieved while keeping the bulk density of the product significantlylower than that of natural stone and solid-surface materials.

In one embodiment, the green intermediate extrudate or cementitiouscomposite can be prepared into a cementitious composite building productas described above. As such, in one embodiment of the cured cementitiouscomposite product can be characterized by having a specific gravityinclusive of pores or cellular formations can be greater than about 1.3or range from about 1.3 to about 3.0, more suitably from about 1.3 toabout 2.3, and most suitably from about 1.6 to about 1.7.

One embodiment of the cured composite can be characterized by having acompressive strength of at least about 6,000 psi, more suitably at leastabout 8,000 psi, and even more suitably at least about 10,000 psi.

In one embodiment, the cured composite can have a flexural strength ofat least about 1,500 psi, more suitably at least about 2,000 psi, moresuitably at least about 3,000 psi, and more suitably at least about4,000 psi, and even more suitably, from about 2,500 psi to about 6,000psi. For example, in one embodiment, the cured composite has a flexuralstrength of up to about 5,700 psi.

With these above strengths, it should be recognized by one skilled inthe art that the cured composites can function as substitutes of naturalstone and solid surface products without the use of reinforcing memberssuch as rebar or glass fibers. This provides for a less expensive andless labor intensive substitute for building materials.

In one embodiment, the cured composite can further have a flexuralmodulus of at least about 500,000, more suitably at least 1,000,000,even more suitably from about 500,000 psi to about 2,000,000 psi, andeven more suitably from about 1,000,000 psi to about 1,750,000 psi.

As noted above, the cured composite further includes a hardness similarto that of stone and other solid-surface materials. More particularly,the cured cementitious composite product includes a hardness of at least4 MOH; more suitably, at least about 5 MOH; more suitably, at leastabout 6 MOH, and even more suitably, from about 7 MOH to about 8 MOH.

EXAMPLES OF EMBODIMENTS OF THE DISCLOSURE Example 1

An extrudable cementitious composition was prepared in accordance withthe present disclosure. The components of the composition were mixedaccording to the normal mixing procedures described above and in thereferences incorporated herein. The extrudable composition wasformulated as illustrated in Table 1.

TABLE 1 Component Amount in Composition Water 11.00 Cement 25.00 PVAfiber 1.25 Silica Sand (#70) 17.50 Methocel ™ (Dow Chemical Company) 1.0Delvo ® Admixture (BASF Construction 0.1 Chemicals) Total 55.85

Following mixing, the composition was extruded through a die head havinga rectangular opening of about 1 inch by about 4 inches. Fourrectangular board samples were prepared. As the first board came out ofthe extruder, it was twisted in opposite directions and placed on a flatsurface. The second board was removed in a plastic hammock and placednext to the first board on the flat surface. The third board was pulleddirectly onto the flat surface with no agitation. All three samplesabove were placed directly into the steam cure chamber to be removed in7 days. The fourth sample was extruded and left to cure on the conveyorwithout any movement or agitation. Various physical properties of theboards were tested after 24 hours, 48 hours, 72 hours, 7 days, and 9days from curing. The results (averaged) are shown in Table 2.

TABLE 2 Property 24 hours 48 hours 72 hours 7 days 9 days Bulk density(g/cc) 1.79 1.85 1.81 1.81 1.85 Flexural Strength 2,563.15 2,374.632,480.58 2,714.57 2,767.62 Flexural Modulus 1,556,360.00 1,499,910.001,577,430.00 1,674,990.00 1,723,940.00 Toughness (psi) 5.01 3.92 3.633.70 4.52

The boards were then visually examined to determine if there was adifference in appearance caused by the different handling methods. Allboards, except for the second board, which was placed into the plastichammock, appeared to contain cracks, however, it was determined that thecracks were silica sand alignment.

Example 2

An extrudable composition for producing a Dahl tile for pavers wasprepared in accordance with the present disclosure. The components ofthe composition were mixed according to the normal mixing proceduresdescribed above and in the references incorporated herein. Theextrudable composition was formulated as illustrated in Table 3.

TABLE 3 Component Amount in Composition Water 14.00 Cement 25.00 PVAfiber 1.50 HW 1.50 Silica Sand (#60) 15.00 Methocel 0.80 Total 57.80 HW= hardwood

After mixing, the composition was extruded. Three samples of theextruded composition were cured in plastic at ambient conditions andthen placed in a steam chamber. The samples were then placed in a dryoven until they reached weight equilibrium. The samples were finallycharacterized by testing bulk density, flexural strength, flexuralmodulus, and toughness. The results are shown in Table 4.

TABLE 4 Average of Property Sample 1 Sample 2 Sample 3 Samples BulkDensity 1.53 1.51 1.53 1.52 (g/cc) Flexural 3,193.90 2,953.90 2,953.712,876.52 Strength (psi) Flexural 1.03 × 10⁶ 1.05 × 10⁶ 1.06 × 10⁶1,044,540.00 Modulus (psi) Toughness 0.85 (psi)

As various changes could be made in the above constructions and methodswithout departing from the scope of the disclosure, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

1. A cementitious composite product having stone-like properties, theproduct comprising an extrudable cementitious composition comprised of ahydraulic cement, aggregate, a rheology-modifying agent, and fiberssubstantially homogeneously distributed through the extrudablecementitious composition and included in an amount greater than about 2%(by volume of the extrudable cementitious composition), wherein thecementitious composite product has a hardness value of at least 4 MOHand a bulk density of at from about 1.3 g/cm³ to about 2.3 g/cm³. 2.-32.(canceled)